Method of employing mercury-dispensing getters in fluorescent lamps

ABSTRACT

A mercury-dispensing getter device is employed in manufacturing a fluorescent lamp by mounting the device within the sealed lamp envelope, flashing the getter by RF induction heat to dispense the mercury, and baking the lamps within an oven at 250*C for two to five minutes to provide gettering of the released and residual gases in the lamp.

United States Patent Waymouth Apr. 17, 1973 METHOD OF EIWPLOYING NIERCURY- 2,322,421 6/l943 DISPENSING GE'I'IERS IN 1;; FLUORESCENT LANIPS 2:896:l87 7/1959 [75] Inventor: John F. Waymouth, Marblehead, 13 1 H1965 Mass 3,317,264 5/1967 L2, WWW A 3,389,288 6/1968 [73] Assignee: GTE Sylvania Incorporated, Dan- 3,475,072 10/1969 vers, Mass.

' Primary Examiner-J. Spencer Overholser [22], FY] led. .June 1971 Assistant Examiner-Richard Bernard Lazarus [21] Appl. No.: 156,707 Attorney-Norman J. OMalley et a1;

. 57 ABSTRACT [52] US. Cl. ....3 16/4, 316/12, 316/25 1 51 Int. Cl .1101 j 9/18, 11013 9/38 A mercurydispensing getter devise is employed in 58 Field of Search ..3 16/1, 17, 1s, 19, manufacturing a fluorescent p y mounting the 31 /20 21 22 24 25 3 4 12; 313/ 74 device within the sealed lamp envelope, flashing the getter by RF induction heat to dispense the mercury, [56] References Cited and baking the lamps within an oven at 250C for two to five minutes to provide gettering of the released UNITED STATES PATENTS and residual gases in the lamp.

2,283,189 5/l942 Cox ..3l3/l8OX 2,288,253 6/1942 Reuter ..250/27.5 8 Claim, 4 Drawing Figures COAT INSIDE ATTACH STEM EXHAUST, APPLY RF BAKE FINISH SURFACE ASSEMBLIES FILL WITH INDUCTION LAMP LAMP OF LAMP INCLUDING RARE GAS, HEAT TO TO ENVELOPE MERCURY AND SEAL DISPENSE GETTER DISPENSING MERCURY GETTER DEVICE PAIENIEDIPRI71975 3.728.004

2 FIG. I 4 IO I 8 A A 4 F G 2 II 3 COAT INSIDE ATTACH STEM EXHAUST; APPLY RF BAKE Q FINISH SURFACE ASSEMBLIES FILL WITH INDUCTION LAMP LAMP OF LAMP INCLUDING RARE GAS, HEAT T0 T0 ENVELOPE MERCURY AND SEAL DISPENSE GETTER DISPENSING MERCURY GETTER I DEVICE JOHN F. WAYMOUTH INVENTOR.

ATTORNEY METHOD OF EMPLOYING MERCURY- DISPENSING GETTERS IN FLUORESCENT LAMPS BACKGROUND OF THE INVENTION This invention relates to the manufacture of electric discharge lamps and more particularly to a method of employing mercury-dispensing getters in the manufacture of fluorescent lamps.

In brief, the conventional manufacturing process for fluorescent lamps proceeds as follows. First a phosphor coating is applied to the inside surface of the lamp envelope, generally by a series of process steps including flushing, drying and curing. Next, a pair of glass stem assemblies, with lead-in wires and electrodes attached, are mounted at each end of the lamp envelope and secured by heat sealing. One or both of the stems include an exhaust tube. An exhaust and gas fill process follows which includes heating the lamp and its cathode electrodes and alternately pumping air from the lamp envelope via the exhaust tubes and flushing with inert gases. At some point, usually toward the end, a drop of mercury is blown into the lamp envelope to provide the necessary source of mercury vapor during subsequent operation of the lamp. At the end of the exhaust process, the lamp is sealed by tipping off the exhaust tubes, and the process is finished by attaching bases and aging.

An alternative method for introducing mercury into the lamp, whichprovides a more accurate control of the quantity inserted, is to mount a mercury-containing device within the lamp envelope and dispense mercury from the device after the lamp is sealed. For example U.S. Pat. No. 2,283,189, issued May 19, 1942, describes a lamp in which a small metal bomb containing the desired quantity of mercury is attached to one of the filament lead-in wires. The mercury remains in the bomb until the lamp is near completion; the bomb is then heated by the filament until the pressure of the heated mercury rises sufficiently to make an opening in the bomb, whereupon the mercury escapes into the lamp.

A more recently developed mercury-containing device for use in fluorescent lamps is that marketed under the trademark GEMED IS by SAES Getters Inc. of Milan, Italy. The GEMED IS device is referred to as a mercury-dispensing getter, since it not only introduces mercury into the lamp, but it also getters residual gases which apparently are generated pursuant to the mercury dispensing process. The device comprises a metal strip containing a composition of mercury, an alloy, and a zirconium-aluminum getter material. The getter strip is attached to the stem assembly of the lamp during manufacture. After the lamp envelope is tipped-off the manufacturer recommends heating the mercury-dispensing getter to a temperature of 90095 C for -30 seconds by RF induction heat to dispense the mercury. The -manufacturer further recommends maintaining the getter at a sufiiciently high temperature, through the RF induction heating, for gettering the gases released at mercury dispensing, together with residual gases in the lamp, for a period sufficient to permit gases to diffuse to the getter through the rare gas fill in the lamp, about 2-5 minutes. It is stated by the manufacturer that it is highly desirable that this be accomplished before even igniting the lamp to prevent formation of chemically very active species from the residual gases because of the action of the discharge.

At lamp production rates of 3,600/hour, heating getters for 2-5 minutes by RF induction heat would require heating getters in -300 lamps at a time, which is clearly impractical. Moreover, because of the extremely high surface area of the phosphor in a lamp, the vast majority of impurity species in a lamp at any given instant of time are sorbed on the phosphor surface rather than in the gaseous phase where they can diffuse to the getter. Thus attempting to clean up residual gases by gettering with the lamp walls at or near room temperature will be ineffective.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide an improved method of using mercurydispensing getters in electric discharge lamps.

It is another object of the invention to provide'an improved and more economical method of post-heating a mercury-dispensing getter for residual gas scavenging in a fluorescent lamp.

Briefly, these object are attained in the manufacturing process of fluorescent lamps containing mercurydispensing getter devices by oven baking the lamps at a relatively low temperature subsequent to flashing of the mercury dispensing devices in the sealed lamp. Processing the lamps through an oven provides a practical and significantly more economical gettering method for mass production manufacturing of lamps. Further, in addition to maintaining the getter at a sufficient temperature to sorb active gases, oven baking also heats the phosphor coating in the lamp to a sufficient temperature to desorb gases therefrom so that they may diffuse to the getter.

BRIEF DESCRIPTION OF THE DRAWING FIG. I is a sectional elevation of a fluorescent lamp manufactured according to the invention;

FIG. 2 is a front plan view of the right hand stem assembly of the lamp of FIG. 1 including a mercurydispensing getter-device mounted thereon;

FIG. 3 is a top view of the assembly of FIG. 2; and

FIG. 4 is a flow diagram of the manufacturing process for the lamp of FIG. 1 in accordance with the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. I, a fluorescent lamp 1 has a sealed, hollow glass envelope 2 containing a filling of argon, although other suitable gas fillings may be used. 0n the inside of the envelope 2, there is a coating 3 of phosphor.

At each end of envelope 2 there is a stem assembly including a sealed glass stem press 4, an electrode comprising an oxide-coated tungsten coil 5, and support and lead-in wires 6 and 7. In addition, the right-hand stem assembly of FIG. 1 includes a mercury-dispensing getter device 8 in the form of a metal strip surrounding coil 5 and supported from the stem press 4 by a wire 9. The usual insulating plastic base 10 with boss 11 carrying contacts 12 and 13 can be as shown in U.S. Pat. No. 2,896,187.

'The mercury-dispensing getter device 8 may be of the type marketed under the trademark GEMED IS by SEAS Getters Inc. of Milan, Italy. It is generally pro- .vided in the form of a metal strip suitable for mounting within a fluorescent lamp, the strip functioning as a carrier for a mercury-dispensing getter material comprising a composition of mercury, an alloy, and a zirconium-alurninum getter material. In one typical configuration, as illustrated by FIGS. 2 and 3, the getter device strip 8 is shaped to surround the electrode coil and is supported by a wire 9 embedded in the glass stern press The process of manufacturing the lamp of FIG. 1 in accordance with the invention is illustrated in FIG. 4. In the first step, a phosphor coating 3 is applied to the inside surface of the lamp envelope 2 according to one of the conventional methods in the art. Next, the stem assemblies, including elements 4 through 9, are attached to the ends of the tubular envelope 2 in the usual manner. A mercury-dispensing getter device 8 may be mounted on just one of the stem assemblies, as shown in FIG. 1, or one may be mounted on each of the stem assemblies. An exhaust and gas fill process then proceeds as is conventional in the art, except that the usual step of blowing a drop of mercury into the lamp is eliminated. At the end of the exhaust process, the lamp is sealed by tipping of the exhaust tubes in the stems.

In the nextstep of the process, the end of the lamp 1 containing the getter device8 is inserted in an RF induction heating coil, and the mercury-dispensing getter material is heated to a temperature of about 900 to 950C for about to 30 seconds. This step of flashing the mercury-containing material carried by device 8 causes the mercury to be dispensed throughout the lamp.

The present invention takes advantage of the fact that once the alloy getter used in the combination mercury-dispensing getter material has been activated by heating to 900-950C, it is capable of sorbing most gaseous species at temperatures as low as 200220C. Such a temperature range is readily accessible to oven baking. According to the present invention, therefore,

. after the above step of flashing the mercury-containing conventional in the art.

Oven baking the lamp after the mercury dispenser flashing step provides several advantages. In contrast to RF induction heating, the phosphor surface as well as the getter device is heated by oven baking, thereby providing significantly more effective gettering of residual gases. Further, the process is more practical and economical for mass production, as an oven can readily accommodate large quantities of lamps at a time. In fact, on a production type of machine, this baking process can be done in an oven over the basing machine, for example, in which the basing cement can be cured as part of the process.

What I claim is:

I. In the manufacture of an electric discharge lamp containing a mercury-dispensing getter means, the 1 steps which comprise:

flashing said mercury-dispensing getter means at a temperature of about 900 to 950C to dispense mercury into said lamp and to activate the getter;

and thereafter baking said lamp in an oven at a temperature of about 200 to 250C for about 2 to 5 minutes to maintain said activated getter at a sufficient temperature to sorb active residual gases and to heat the lamp sufficiently to desorb gases from the interior surface thereof;

said foregoing steps being performed prior to the initial igntion of said lamp.

2. The process of claim 1 wherein said flashing step comprises heating said mercury-dispensing getter means to a temperature of about 900 to 950C for about 20 to 30 seconds by RF induction heat.

3. The process of claim 2 wherein said lamp is a fluorescent lamp.

4. The process of claim 1 further including a step prior to said baking step which comprises cementing bases to the ends of said lamp, and wherein said basing cement is cured during said baking step.

5. In the manufacture of a fluorescent lamp having a glass envelope, the steps which comprise:

coating the inside surface of said glass envelope with phosphor;

attaching stem assemblies to the ends of said e'nvelope, each stem assembly including an electrode, and at least one of said stern assemblies including a mercury-dispensing getter means; exhausting said envelope, and filling said envelope with a rare gas;

sealing said envelope;

flashing said mercury-dispensing getter means to dispense mercury into said sealed envelope and to activate the getter;

and thereafter baking said lamp in an oven for about 2 to 5 minutes to maintain said activated getter at a sufficient temperature to sorb active residual gases and to heat said envelope sufficiently to desorb gases from said phosphor coating;

said foregoing steps being performed prior to the initial ignition of said lamp.

6. The process of claim 5 wherein said flashing step comprises heating said mercury-dispensing getter means to a temperature of about 900 to 950C for about 20 to 30 seconds by RF induction heat.

7. The process of claim 6 wherein said baking performed at about 250C 8. The process of claim 7 further including a step prior to said baking step which comprises cementing bases to the ends of said lamp, and wherein said basing cement is cured during said baking step.

step is 

1. In the manufacture of an electric discharge lamp containing a mercury-dispensing getter means, the steps which comprise: flashing said mercury-dispensing getter means at a temperature of about 900* to 950*C to dispense mercury into said lamp and to activate the getter; and thereafter baking said lamp in an oven at a temperature of about 200* to 250*C for about 2 to 5 minutes to maintain said activated getter at a sufficient temperature to sorb active residual gases and to heat the lamp sufficiently to desorb gases from the interior surface thereof; said foregoing steps being performed prior to the initial igntion of said lamp.
 2. The process of claim 1 wherein said flashing step comprises heating said mercury-dispensing getter means to a temperature of about 900* to 950*C for about 20 to 30 seconds by RF induction heat.
 3. The process of claim 2 wherein said lamp is a fluorescent lamp.
 4. The process of claim 1 further including A step prior to said baking step which comprises cementing bases to the ends of said lamp, and wherein said basing cement is cured during said baking step.
 5. In the manufacture of a fluorescent lamp having a glass envelope, the steps which comprise: coating the inside surface of said glass envelope with phosphor; attaching stem assemblies to the ends of said envelope, each stem assembly including an electrode, and at least one of said stem assemblies including a mercury-dispensing getter means; exhausting said envelope, and filling said envelope with a rare gas; sealing said envelope; flashing said mercury-dispensing getter means to dispense mercury into said sealed envelope and to activate the getter; and thereafter baking said lamp in an oven for about 2 to 5 minutes to maintain said activated getter at a sufficient temperature to sorb active residual gases and to heat said envelope sufficiently to desorb gases from said phosphor coating; said foregoing steps being performed prior to the initial ignition of said lamp.
 6. The process of claim 5 wherein said flashing step comprises heating said mercury-dispensing getter means to a temperature of about 900* to 950*C for about 20 to 30 seconds by RF induction heat.
 7. The process of claim 6 wherein said baking step is performed at about 250*C.
 8. The process of claim 7 further including a step prior to said baking step which comprises cementing bases to the ends of said lamp, and wherein said basing cement is cured during said baking step. 